Process of making nitric acid.



UNITED STATES PATENT OFFICE.

PROCESS OF MAKING NITRIC ACID.

Specification of Letters Patent.

Patented Aug. 29, 1905.

Application filed May 25, 1904. Serial No. 209,745.

To all whmn it Wen/y concern.-

Be it known that I, HEINRICH HUGO NIE- DENFUHR, chemical engineer, a subject of the German Emperor, residing at 4 1 Joachim- Friedrichstrasse, in the town of Halensee, near Berlin, Kingdom of ,Prussia, German Empire, have invented a certain new and useful Process of Manufacturing Nitric Acid, of which the following is a specification.

, This invention refers to a process for manufacturing nitric acid by means of which it is possible to efl ect a practically perfect condensation of the nitric-acid vapors and the removal of the lower oxids of nitrogen, the latter being at the same time submitted to a practically complete condensation and oxidation into nitric acid.

For the. purpose of obtaining nitric acid of very great acid strength and of a very high degree of purity it is necessary to so regulate the condensing operation that the condensation product is prevented from being acted upon by the simultaneously formed lower oxids of nitrogen as soon as it is formed. Besides, the condensation has to take place at as high a temperature as possible in order to facilitate the bleaching of the acid, while at the same time care has to be taken to avoid the condensation of water-vapors and also to prevent the absorption of the lower oxids of nitrogen. It is also of essential importance to have the gases pass as quickly as possible through the pipe-conduits, so that the liquid 1 can remain only for a Very short time in contact with the vapors. On the other hand, the

oxidation and condensation of the escaping,

lower oxids of nitrogen, however, calls for the retaining of the gases in the condensingchambers for a rather long time, and it also necessitates the contact of the said gases with the liquid formed, the contact presenting no inconveniences in this stage, because the acid produced from the lower oxids of nitrogen is not submitted to the bleaching operation. In this stage the contact of gases and liquid greatly aids in facilitating and completing the oxidation. Hence it follows that for obtaining the maximum of yield and for producing a light-colored product at the same time it becomes necessary to force the gases as quickly as possible through one part of the apparatus and to separate them from the liquid at a comparately high temperature, while in the other part of the apparatus the gases should be retained as long as possible and have to be brought into contact with the liquid produced at a correspondingly lower temperature. With the arrangements heretofore employed for the manufacture of nitric acid this effect could not be produced, because the draft-generator for effecting the rapid withdrawal of the gases from that part of the plant directly connected to the acid-generating vessel was arranged at the end of the entire system, so that even the gases in the condensing-chamhers for the lower nitrogen oxids were also forced through the system. Moreover, when working in this manner it was difficult to obtain a regulation of the temperature in the several parts of the system; nor was it possible to accomplish the desired result by forcing compressed air into the nitricacid vapors evolved from the acid-generating vessel, as has been suggested heretofore, the

draft-generator being thus inserted between the acid-generating vessel and the condensing plant, so to speak. When proceeding in this manner, there was also a rather uniform pressure all throughout the entire system, the pressure decreasing even toward the end of the system instead of being higher at the end of the system than in the part immediately adjoining the acid-generating vessel, as would be required by the fact that the lower oxids of nitrogen are to be oxidized and condensed at the end of the system. Besides, in this previously-practiced process and in other processes as heretofore employed there was an undue dilution of the gases before they went to the condensing part of the plant on account of the exceedingly-great volume of air which was forced either into the generatingchamber directly or into the connecting means between the generator and the condensing apparatus, whereby condensation was rendered very difficult and the gases acquired too large a volume to handle them in ordinary-sized plants. In my invention, however, this dilution by air or other gases or vapors is excluded in this part of the plant. My invention is, moreover, distinguished from these prior ways of procedure by arranging the draft-generator behind that part of the system where the condensation of the nitric-acid vapors is eifected,and which is directly connected to the acid-generating vessel and before that part of the plant which serves for the oxidation and condensation of the lower oxids of nitrogen. By suitably regulating the dimensions of the several parts of the plant aslight ing the two parts of the plant, which have to accomplish entirely-different functions, from each other by the draft or pressure generator, preferably a fan or ventilator, the regulation of the temperature in the several parts of the system is also facilitated. It is thus possible to impart as high as possible a tem.

perature to that part of the plant or system adjoining the acid-generating chamber, the generated acid at this high temperature taking up but a very slight percentage of lower oxids of nitrogen, which are easily given off from the liquid again, so that the acid can be easily bleached and the very strongest acid is produced in this part of the plant. Before the gases are caused to enter into the second part of the system, where the lower oxids of nitrogen are submitted to the process of oxidation and condensation, and preferably before the gases are allowed to enter into the draft or pressure generator, it is recommendable to submit the gases to a strong cooling operation in a suitable small condensing appara tus, partly for the purpose of preventing wear and destruction-of the pressure-generating device and for producing as low a temperature as possible in the following part of the apparatus and then for the purpose of precipitating the not yet condensed fractions of nitric acid from the vapors though in an impure state. By proceeding in this manner the vapors are caused to enter at a low tem perature and under high pressure into the chambers intended for carrying on the oxidation and condensation of the lower oxids of nitrogen, the said chambers or vessels, as already mentioned, being of maller size than those parts of the system adjoining the acidgenerating vessel. It is of ad vantage to keep the nitric acid produced in this last part of the apparatus as hot as possible also in the collecting vessels into which the said acid is allowed to run, so as to be able to effect the bleaching and the subsequent purification of the said acid in the well-known manner by blowing air through it.

By proceedingin this manner that is to say, by carrying out the process in two stages 1t is possible to obtain a very high yield of nitric acid and to manufacture highly-concentrated commercially-pure nitric acid and to convert the lower oxids of nitrogen also into nitric acid in one and the same apparatus and simultaneously with the production of pure acid.

What I claim, and desire to secure by Letters Patent of the United States, is-- 1. The process of manufacturing nitric acid, which consists in treating any suitable combination of nitric acid with nitric-acid-evolving reagents, generating concentrated, undiluted fumes of a mixture of higher and lower oxids of nitrogen, condensing and liquefying into nitric acid the said higher oxids of nitrogen in a concentrated state and out of contact with the said fumes-generating substance, immediately separating the uncondensed lower oxids of nitrogen. from the liquid nitric acid, submitting said gaseous lower oxids to an increase of pressure and condensing and liquefying the same separately from the previously condensed and liquefied bullg of nitric acid.

2. The process of manufacturing nitric acid, which consists in treating any suitable nitrate with nitric-acid-liberating reagents and practically in the absence of air, then condensing the fumes evolved in a concentrated and undiluted state and at a comparatively high temperature and out of contact with said nitrate separating the liquefied nitric acid from the gaseous lower oxids of nitrogen and preventing any substantial absorption of the same by the liquid formed, then submitting said lower oxids to pressure and condensing said lower oxids and liquefying the same and treating said liquefied lower oxids with air.

3. The process of manufacturing nitric acid which consists in treating any suitable nitrate with nitric-acid-evolving acid and practically in the absence of foreign oxidizing agents, condensing part of the concentrated and undiluted fumes evolved out of contact with said nitrate and at a comparatively high temperature and at a somewhat reduced pressure, separating the condensed and liquefied portion, consisting of nitric acid, quickly from the uncondensed fumes of lower oxids of nitrogen, submitting said lower oxids to pressure and condensing said lower oxids and practically liquefying the same and treating the liquefied lower oxids with air and bleaching said lower oxids in a liquefied state and out of contact with the previously condensed and liquefied nitric acid.

4. The process of manufacturing nitric acid, which consists in treating nitrates with suitable nitric-acid-evolving acids and practically without foreign oxidizing agents, then submitting the concentrated and undiluted fumes evolved to a process of condensation and liquefaction at a comparatively high temperature and at a somewhat reduced pressure, quickly separating the liquefied portion, consisting of nitric acid, from the unliquefied, gaseous lower oxids of nitrogen, preventing undue abtrogen and submitting them to an increase of pressure and condensing and practically liquefying the same out of contact with the previously condensed and liquefied nitric acid, oxidizing the liquefied lower oxids and lightening the color of the same.

5. The process herein described of manufacturing nitric acid, which consists in treating nitrates with a suitable acid and generating fumes of oxids of nitrogen substantially without foreign oxidizing agents, treating the concentrated and undiluted fumes evolved to an immediate condensation process out of contact with said nitrates at a comparatively high temperature and at a somewhat-reduced pressure separating the condensed and liquefied nitric acid from the uncondensed gaseous lower oxids of nitrogen and preventing any substantial absorption of the said oxids by the liquid, then condensing said gaseous lower oxids of nitrogen at alower temperature and at an increased pressure and in contact with the liquefied portion of said gaseous oxids, keeping said lower oxids under pressure and at a low temperature until practically all of the gas is condensed and collecting the resulting liquefied lower oxids and oxidizing the same. 1

In testimony whereof I have set my hand to this specification in the presence of two subscribing witnesses.

HEINRICH HUGO NIEDENFUHR.

Witnesses:

HENRY HASPER, WOLDEMAR HAUPT. 

